Pioneer 1, the second and most successful of three project Able space probes and the first spacecraft launched by the newly formed NASA, was intended to study the ionizing radiation, cosmic rays, magnetic fields, and micrometeorites in the vicinity of the Earth and in lunar orbit. Due to a launch vehicle malfunction, the spacecraft attained only a ballistic trajectory and never reached the Moon. It did return data on the near-Earth space environment.

Spacecraft and Subsytems

Pioneer 1 consisted of a thin cylindrical midsection with a squat truncated cone frustrum on each side. The cylinder was 74 cm in diameter and the height from the top of one cone to the top of the opposite cone was 76 cm. Along the axis of the spacecraft and protruding from the end of the lower cone was an 11 kg solid propellant injection rocket and rocket case, which formed the main structural member of the spacecraft. Eight small low-thrust solid propellant velocity adjustment rockets were mounted on the end of the upper cone in a ring assembly which could be jettisoned after use. A magnetic dipole antenna also protruded from the top of the upper cone. The shell was composed of laminated plastic. The total mass of the spacecraft after vernier separation was 34.2 kg, after injection rocket firing it would have been 23.2 kg.

The scientific instrument package had a mass of 17.8 kg and consisted of an image scanning infrared television system to study the Moon's surface to a resolution of 1 milliradian, an ionization chamber to measure radiation in space, a diaphragm/microphone assembly to detect micrometeorites, a spin-coil magnetometer to measure magnetic fields to 5 microgauss, and temperature-variable resistors to record spacecraft internal conditions. The spacecraft was powered by nickel-cadmium batteries for ignition of the rockets, silver cell batteries for the television system, and mercury batteries for the remaining circuits. Radio transmission was at on 108.06 MHz through an electric dipole antenna for telemetry and doppler information at 300 mW and a magnetic dipole antenna for the television system at 50 W. Ground commands were received through the electric dipole antenna at 115 MHz. The spacecraft was spin stabilized at 1.8 rps, the spin direction was approximately perpendicular to the geomagnetic meridian planes of the trajectory.


Ion Chamber The ion-chamber experiment was designed to study the high flux radiation surrounding the earth. The instrument was an aluminum-walled, cylindrically shaped vessel with a volume of 43 cubic cm filled with spectroscopically pure argon. It was mounted just inside the cylindrical wall of the satellite. The minimum areal density that a particle traversed before reaching the sensitive volume of the chamber was 0.45 gm/sq cm, the maximum was 20 gm/sq cm. The current from the ion chamber was measured by a DC electrometer amplifier with a range of 0.5 Roentgens/hr to 1E7 Roentgens/hr. The duty cycle of the instrument consisted of 180 sec of ionization chamber output followed by 20 sec of calibration voltage. The chamber was capable of responding to primary cosmic rays and also to the secondary mesons, protons, beta particles, and gamma rays that may result from the interaction of the primary particles with the walls of the chamber and the material surrounding the ion chamber. The secondaries could increase the ionization a factor of 50. Electrons must have an energy greater than 1 MeV, protons greater than 5 MeV, and alphas greater than 200 MeV in order to penetrate the walls of the chamber. It was discovered that the ion chamber had leaked and that the pressure during flight was 1.58 atmospheres. Consideration of all other errors resulted in a standard deviation as great as 50 percent for some data points. Most of the data were transmitted from 1000 to 1800 UT on October 11, 1958, and from 0800 to 2100 UT on October 12, 1958. See Rosen et al, JGR, vol 64, p 709, 1959, for further details and for resultant data.

Single Axis Search-Coil Magnetometer This magnetometer was designed to study the magnetic field between the earth and the moon and to test for a lunar magnetic field. Due to a launch vehicle malfunction, it was used to study the geomagnetic field along the trajectory. The magnetometer was a single search coil designed to measure the component of the magnetic field perpendicular to the spin axis. The returned signal was digitized at 52 samples per sec. The magnetometer had a range of 6 microgauss to 12 milligauss. No inflight calibration was provided between 0945 and 1106 UT and between 1543 and 1719 UT when the spacecraft was at radial distances of 3.7 to 7.0 and 12.3 to 14.8 earth radii. The experiment is described in detail by Sonett, JGR, vol 67, p 1191, 1962.


A diaphragm/microphone micrometeorite detector assembly that permitted a two-level discrimination of impact energy was designed to determine micrometeorite density in interstellar space. The area of the exterior diaphragm equaled a predetermined fraction of the total surface area of the spacecraft. Results were limited because of a vehicle failure which caused the spacecraft to reenter the atmosphere over the South Pacific on October 12, 1958.

Launch-Orbit Information

Launch Date: 1958-10-11 at 08:42:00 UTC
Launch Vehicle: Thor-Able
Launch Site: Cape Canaveral, United States
Decay Date: 1958-10-13
Mass: 34.2 kg